Type	Purpose	Example
Trigger	Ethereal zones (no physics)	Pickups, damage zones, checkpoints
Collision	Solid interactions (physics)	Bouncy pads, walls, platforms

Trigger vs Collision

Trigger:
- Player passes through
- No physical bump
- Requires: Collider with "Is Trigger" = true

Collision:
- Player bumps into object
- Physical interaction
- Requires: Collider + Rigidbody on moving object

Triggers

Interface: `Component.ITriggerListener`

Used for zones that detect entry/exit without blocking movement.

Requirements

GameObject must have a Collider (Box, Sphere, Capsule)
Collider must have "Is Trigger" enabled
Component must implement Component.ITriggerListener

Methods

void OnTriggerEnter(Collider other)  // Object enters zone
void OnTriggerExit(Collider other)   // Object leaves zone

Basic Trigger Example

using Sandbox;

public sealed class HealZone : Component, Component.ITriggerListener
{
    [Property] public float HealAmount { get; set; } = 10f;
    [Property] public float HealInterval { get; set; } = 1f;
    
    public void OnTriggerEnter(Collider other)
    {
        Log.Info($"{other.GameObject.Name} entered heal zone");
        
        var player = other.GameObject.Components.Get<PlayerController>();
        if (player != null)
        {
            player.Heal(HealAmount);
        }
    }
    
    public void OnTriggerExit(Collider other)
    {
        Log.Info($"{other.GameObject.Name} left heal zone");
    }
}

Scene Setup for Triggers

Create GameObject (Cube, Sphere, etc.)
Add Box Collider (or Sphere Collider)
Enable "Is Trigger" checkbox
Attach your trigger component

GameObject: HealPad
├── Box Collider (Is Trigger: ✓)
└── HealZone Component

Collisions

Interface: `Component.ICollisionListener`

Used for solid interactions where objects physically bump into each other.

Requirements

GameObject must have a Collider
Moving object (e.g., Player) must have a Rigidbody
Component must implement Component.ICollisionListener

Critical: At least one object in the collision must have a Rigidbody component.

Methods

void OnCollisionStart(Collision collision)   // Collision begins
void OnCollisionUpdate(Collision collision)  // Collision ongoing
void OnCollisionStop(Collision collision)    // Collision ends

Basic Collision Example

using Sandbox;

public sealed class BouncyPad : Component, Component.ICollisionListener
{
    [Property] public float Bounciness { get; set; } = 500f;
    
    public void OnCollisionStart(Collision collision)
    {
        Log.Info($"Collision with {collision.Other.GameObject.Name}");
        
        var player = collision.Other.GameObject.Components.Get<PlayerController>();
        if (player != null)
        {
            // Launch player upward
            player.Velocity = player.Velocity.WithZ(Bounciness);
        }
    }
    
    public void OnCollisionUpdate(Collision collision)
    {
        // Called every frame while colliding
    }
    
    public void OnCollisionStop(Collision collision)
    {
        // Called when collision ends
    }
}

Player Rigidbody Setup

For collisions to work with Character Controllers:

// Player component setup
[RequireComponent] CharacterController Controller { get; set; }
[RequireComponent] Rigidbody Body { get; set; }

protected override void OnStart()
{
    // Make Rigidbody "inert" - doesn't interfere with movement
    Body.Gravity = false;
    Body.LockAxes = RigidbodyAngularLockMode.All;
}

Scene Setup for Collisions

Create GameObject (platform, obstacle)
Add Collider (not trigger)
Ensure Player has Rigidbody
Attach your collision component

GameObject: BouncyPlatform
├── Box Collider (Is Trigger: ✗)
└── BouncyPad Component

GameObject: Player
├── Character Controller
├── Rigidbody (Gravity: Off, Lock Axes: All)
└── PlayerController Component

Accessing Collision Data

From Collider (Triggers)

public void OnTriggerEnter(Collider other)
{
    // Get GameObject
    var go = other.GameObject;
    
    // Get specific component
    var player = other.GameObject.Components.Get<PlayerController>();
    
    // Check if component exists
    if (other.GameObject.Components.TryGet<Health>(out var health))
    {
        health.TakeDamage(10);
    }
}

From Collision

public void OnCollisionStart(Collision collision)
{
    // Get the other GameObject
    var other = collision.Other.GameObject;
    
    // Get collision point
    var contact = collision.Contact;
    Vector3 position = contact.Point;
    Vector3 normal = contact.Normal;
    
    // Get component from other object
    var player = other.Components.Get<PlayerController>();
}

Practical Examples

Checkpoint System

public sealed class Checkpoint : Component, Component.ITriggerListener
{
    [Property] public int CheckpointID { get; set; }
    [Property] public bool IsActivated { get; set; } = false;
    
    public void OnTriggerEnter(Collider other)
    {
        var player = other.GameObject.Components.Get<Player>();
        if (player != null && !IsActivated)
        {
            IsActivated = true;
            player.SetRespawnPoint(GameObject.Transform.Position);
            Log.Info($"Checkpoint {CheckpointID} activated!");
        }
    }
    
    public void OnTriggerExit(Collider other) { }
}

Damage Zone

public sealed class DamageZone : Component, Component.ITriggerListener
{
    [Property] public float Damage { get; set; } = 10f;
    [Property] public float DamageInterval { get; set; } = 1f;
    
    private Dictionary<GameObject, TimeSince> _damageTimes = new();
    
    public void OnTriggerEnter(Collider other)
    {
        if (other.GameObject.Components.TryGet<Health>(out var health))
        {
            _damageTimes[other.GameObject] = 0;
        }
    }
    
    protected override void OnUpdate()
    {
        foreach (var kvp in _damageTimes.ToList())
        {
            if (kvp.Value > DamageInterval)
            {
                if (kvp.Key.Components.TryGet<Health>(out var health))
                {
                    health.TakeDamage(Damage);
                    _damageTimes[kvp.Key] = 0;
                }
            }
        }
    }
    
    public void OnTriggerExit(Collider other)
    {
        _damageTimes.Remove(other.GameObject);
    }
}

Jump Pad

public sealed class JumpPad : Component, Component.ICollisionListener
{
    [Property] public Vector3 LaunchVelocity { get; set; } = new Vector3(0, 0, 800);
    [Property] public string SoundEffect { get; set; } = "jumppad";
    
    public void OnCollisionStart(Collision collision)
    {
        var controller = collision.Other.GameObject.Components.Get<CharacterController>();
        if (controller != null)
        {
            // Launch player
            controller.Velocity = LaunchVelocity;
            
            // Play sound
            Sound.Play(SoundEffect, GameObject.Transform.Position);
        }
    }
    
    public void OnCollisionUpdate(Collision collision) { }
    public void OnCollisionStop(Collision collision) { }
}

Collectible Pickup

public sealed class Coin : Component, Component.ITriggerListener
{
    [Property] public int Value { get; set; } = 1;
    [Property] public string PickupSound { get; set; } = "coin";
    
    public void OnTriggerEnter(Collider other)
    {
        var player = other.GameObject.Components.Get<Player>();
        if (player != null)
        {
            // Give player coins
            player.AddCoins(Value);
            
            // Play sound
            Sound.Play(PickupSound, GameObject.Transform.Position);
            
            // Destroy this coin
            GameObject.Destroy();
        }
    }
    
    public void OnTriggerExit(Collider other) { }
}

Moving Platform (Collision)

public sealed class MovingPlatform : Component, Component.ICollisionListener
{
    [Property] public Vector3 MoveDistance { get; set; } = new Vector3(0, 0, 100);
    [Property] public float MoveSpeed { get; set; } = 50f;
    
    private Vector3 _startPosition;
    private HashSet<GameObject> _ridingObjects = new();
    
    protected override void OnStart()
    {
        _startPosition = GameObject.Transform.Position;
    }
    
    protected override void OnFixedUpdate()
    {
        // Oscillate position
        float t = (float)Math.Sin(Time.Now * MoveSpeed * 0.01f);
        GameObject.Transform.Position = _startPosition + MoveDistance * t;
        
        // Move riding objects with platform
        foreach (var obj in _ridingObjects)
        {
            if (obj.IsValid())
            {
                var controller = obj.Components.Get<CharacterController>();
                if (controller != null)
                {
                    controller.Velocity += MoveDistance * MoveSpeed * Time.Delta;
                }
            }
        }
    }
    
    public void OnCollisionStart(Collision collision)
    {
        _ridingObjects.Add(collision.Other.GameObject);
    }
    
    public void OnCollisionUpdate(Collision collision) { }
    
    public void OnCollisionStop(Collision collision)
    {
        _ridingObjects.Remove(collision.Other.GameObject);
    }
}

Common Pitfalls

Trigger Not Firing

// ❌ Forgot to enable "Is Trigger"
// Solution: In scene, select GameObject → Box Collider → Is Trigger: ✓

// ❌ Didn't implement interface
public class MyTrigger : Component { } // Missing : Component.ITriggerListener

// ✅ Correct
public class MyTrigger : Component, Component.ITriggerListener { }

Collision Not Working

// ❌ Player missing Rigidbody
// Solution: Add Rigidbody to player GameObject

// ❌ Rigidbody interfering with movement
// Solution: Disable gravity and lock axes
protected override void OnStart()
{
    Body.Gravity = false;
    Body.LockAxes = RigidbodyAngularLockMode.All;
}

// ❌ Collider set to "Is Trigger"
// Solution: Uncheck "Is Trigger" for solid collisions

Null Reference

// ❌ Crashes if component doesn't exist
var player = other.GameObject.Components.Get<Player>();
player.Health += 10; // Null reference!

// ✅ Safe check
var player = other.GameObject.Components.Get<Player>();
if (player != null)
{
    player.Health += 10;
}

// ✅ TryGet pattern
if (other.GameObject.Components.TryGet<Player>(out var player))
{
    player.Health += 10;
}

Advanced Patterns

Tag-Based Filtering

public sealed class PlayerOnlyTrigger : Component, Component.ITriggerListener
{
    [Property] public string RequiredTag { get; set; } = "Player";
    
    public void OnTriggerEnter(Collider other)
    {
        if (other.GameObject.Tags.Has(RequiredTag))
        {
            // Only trigger for objects with "Player" tag
            HandlePlayerEnter(other.GameObject);
        }
    }
    
    public void OnTriggerExit(Collider other) { }
}

Layered Collision Response

public sealed class MultiResponsePlatform : Component, Component.ICollisionListener
{
    public void OnCollisionStart(Collision collision)
    {
        var go = collision.Other.GameObject;
        
        // Different responses for different components
        if (go.Components.TryGet<Player>(out var player))
        {
            player.Velocity = player.Velocity.WithZ(500);
        }
        else if (go.Components.TryGet<Enemy>(out var enemy))
        {
            enemy.TakeDamage(100);
        }
        else if (go.Components.TryGet<Projectile>(out var projectile))
        {
            projectile.Destroy();
        }
    }
    
    public void OnCollisionUpdate(Collision collision) { }
    public void OnCollisionStop(Collision collision) { }
}

One-Time Trigger

public sealed class OneTimeTrigger : Component, Component.ITriggerListener
{
    [Property] public bool HasTriggered { get; set; } = false;
    
    public void OnTriggerEnter(Collider other)
    {
        if (HasTriggered) return;
        
        var player = other.GameObject.Components.Get<Player>();
        if (player != null)
        {
            HasTriggered = true;
            // Do one-time action
            player.UnlockAbility("DoubleJump");
        }
    }
    
    public void OnTriggerExit(Collider other) { }
}

Exploring More Interfaces

S&box provides many component interfaces. Discover them by typing Component.I in your IDE:

Component.ITriggerListener - Trigger zones
Component.ICollisionListener - Collision detection
Component.ITintable - Color tinting
Component.INetworkSpawnable - Network spawning
And more...

Quick Reference

Trigger Template

using Sandbox;

public sealed class MyTrigger : Component, Component.ITriggerListener
{
    public void OnTriggerEnter(Collider other)
    {
        // Object entered
    }
    
    public void OnTriggerExit(Collider other)
    {
        // Object exited
    }
}

Scene Setup:

Add Collider
Enable "Is Trigger"
Attach component

Collision Template

using Sandbox;

public sealed class MyCollision : Component, Component.ICollisionListener
{
    public void OnCollisionStart(Collision collision)
    {
        // Collision started
    }
    
    public void OnCollisionUpdate(Collision collision)
    {
        // Collision ongoing
    }
    
    public void OnCollisionStop(Collision collision)
    {
        // Collision ended
    }
}

Scene Setup:

Add Collider (not trigger)
Ensure player has Rigidbody
Attach component

Resources

S&box Wiki: Scene System Documentation
API Reference: Component Interfaces
Video Tutorial: S&box Triggers & Collisions 2024
Component Discovery: Type Component.I in IDE to see all interfaces

Trigger vs Collision

Triggers

Interface: Component.ITriggerListener

Requirements

Methods

Basic Trigger Example

Scene Setup for Triggers

Collisions

Interface: Component.ICollisionListener

Requirements

Methods

Basic Collision Example

Player Rigidbody Setup

Scene Setup for Collisions

Accessing Collision Data

From Collider (Triggers)

From Collision

Practical Examples

Checkpoint System

Damage Zone

Jump Pad

Collectible Pickup

Moving Platform (Collision)

Common Pitfalls

Trigger Not Firing

Collision Not Working

Null Reference

Advanced Patterns

Tag-Based Filtering

Layered Collision Response

One-Time Trigger

Exploring More Interfaces

Quick Reference

Trigger Template

Collision Template

Resources

Interface: `Component.ITriggerListener`

Interface: `Component.ICollisionListener`

sbox-triggers-collisions

S&box Triggers & Collisions

When to Use

Core Concepts